Data flows connected to SQL are not refreshing on schedule but refreshing manually.

Prasanth460 

This is more likely your credential mapping between PBI service and gateway configuration connection.
You need to verify this step by step.
1- Configure Gateway connection with your local a/c and test the connection, if this successfull it means we have diagnose correctly. 

Data source type = SQL Server
Gateway connection = your enterprise gateway
Authentication method = Windows / Basic / OAuth (depending on your setup)
User name = service account or local a/c

2          Dataflow credential settings in Power BI Service.

            Sometimes Dataflow uses cached credentials. That can cause a problem during PBI refresh settings.

3          Gateway SQL data source mapping.

            Gateway SQL data source mapping issue

4          Service account password/lock status

5          Parent dataflow credentials

            If you are using nested dataflow, then you might need to check parent dataflow connection settings.

6         Gateway logs
           Finally, the Gateway logs needs to be verified, as you DBA he will check the on prem Gateway logs by 

          running few commands.

If this helps, ✓ Mark as Kudos | Help Others